Analog-to-digital converters (ADCs) convert analog signals to discrete digital signals for processing by digital electronics. For example, an ADC may be used to convert an analog audio input from a microphone to a digital signal for processing and manipulation by a digital processor, such as a microprocessor or a digital signal processor (DSP). One example of a conventional ADC is shown in FIG. 1.
An ADC 100 may receive an input signal, Vin, for conversion to a digital signal. The input signal, Vin, may range, for example, between 0 and 5 Volts. The ADC may convert the input signal, Vin, to a digital output signal, OUT, through a plurality of comparators 102A-N. The digital output signal, OUT, may have N bits corresponding to the number of comparators 102A-N. Each of the comparators 102A-N compare the input signal, Vin, to a reference level that is a fraction of a reference input, Vref, defined by resistors 104A-N. For example, when the input signal, Vin, ranges from 0 to 5 Volts, and there are four comparators, the comparator 102A may compare the input voltage, Vin, to 3.75 Volts, the comparator 102B may compare the input signal, Vin, to 2.5 Volts, the comparator 102C may compare the input signal, Vin, to 1.25 Volts, and the comparator 102N may compare the input signal, Vin, to 0 Volts. Each of the comparators 102A-N may output a zero value if the input signal, Vin, is not higher than 3.75, 2.5, 1.25, and 0 Volts, respectively. Likewise, each of the comparators 102A-N may output a one value if the input signal, Vin, is higher than 3.75, 2.5, 1.25, and 0 Volts, respectively. Thus, when the input signal, Vin, is 3.0 Volts, the output digital signal, OUT, would be “0111.” Accuracy may be improved in the ADC 100 by, for example, increasing the number of comparators 102A-N.
In the example provided above, each of the comparators 102A-N is continuously comparing the input signal, Vin, to a reference level. Thus, each of the comparators 102A-N is consuming power, despite the fact that the outputs of some of the comparators 102A-N may rarely change. In the example described above, the input signal, Vin, may range between 0 and 5 Volts, but generally remains around 2.5-3.0 Volts. For such a signal, the comparators 102A and 102B may be sufficient for part of the time to generate the digital output signal, OUT, and the comparators 102C and 102D may be powered down.
Conventional tracking ADCs are one type of ADC that focuses on conversion of a small sampling region. A tracking ADC may activate comparators around a region of interest and power down other comparators of the comparators 102A-N to reduce power consumption by the ADC 100. For example, in a flash type of tracking ADC, only comparators with a reference level close to a voltage level of the input signal, Vin, may be turned on during normal operation. A control signal, CTRL, may be used to turn on and turn off the comparators 102A-N in this type of ADC.
Conventional tracking ADCs may also, for example, shuffle sensing components of the ADC or manipulate the input signal, Vin, to adapt the tracking range of the ADC to improve tracking accuracy or resolution. For example, shuffling sensing components of the ADC may include implementing a window tracking feature, which turns on a set number of the comparators 102A-N, such as four comparators, and then shifts which four comparators are powered on based on a level of the input signal, Vin. In another example, adapting the tracking range of the ADC may include changing the reference level of the comparators 102A-N, such as by varying a resistance of the resistors 104A-N. However, both of these conventional tracking ADCs have fixed numbers of active comparators of the comparators 104A-N. This reduces the flexibility of the ADC to respond to a rapidly changing input signal, Vin, while also placing a limit of the power savings potential of the tracking ADC.
Shortcomings mentioned here are only representative and are included simply to highlight that a need exists for improved analog-to-digital converters (ADCs), particularly for consumer-level devices. Embodiments described here address certain shortcomings but not necessarily each and every one described here or known in the art.